Instrument for measuring distances optically.



B. -A. FISKE.

/ INSTRUMENT FOR MEASURING DISTANCES OPTICALLY. I APPLICATION FILED MAYIO, I915. 4

1,208,120. Patented Dec. 12,1916.

A TTORNEYS B. A. FISKE.

INSTRUMENT FOR MEASURING DISTANCES OPTICALLY.

APPLICATION 11.51) MAY 10. 1915.

1,208,120- Patented De0.12, 1916.

2 SHEETS SHEIET 2.

FTCDB.

INVENTOR A TTORNEIS UNITED STATES PATENT OFFICE.

BRADLEYA. FISKE, on THE UNITED STATES 'NAVY, ASSIGNOR TO BAUSCH & LOMB OPTICAL COMPANY, or ROCHESTER, NEW YORK, A CORPORATION on NEW YORK.

INSTRUMENT FOR MEAsUBIitG-DIsTANons OPTICALLY.

Patented Dec. 12, 1916.

Application filed May 10, 1915. Serial No. 26,932.

To allu-iwm it may concern;

lie it known that 11. Brennan A. Fisnn, a citizen of the. luited States, and Hear Ad miral ot' the United States Navy,.a11d residing at Washington, in the District; of Coluinhia', have invented eertainnew and useful Improvements in Instruments for 'liieasuringr Distances Optically; and I do that it suhtends and more particularlyrelates to that class of instrument wherein the.

distance oi an object from the position of the instrumentn n\ v he delta-mined from the size ot' sa id ohjeets image. formed on the focal plane of the instrument, provided one dimension of the object in a plane that is substantially parallel to the said focal plane,

is'known. '.()h eets ot the present invention are: to provide an improved distance measur ng 111- strlunent which is capable of greater a c eurary and better consistency oi measuring,

which is more widely nseiul and which gives a lielter illuminated image than instruments heretofore knowuaml used for similar measuring purposes.-

()tlier ohjeets olithis invention will'hereinai'ter heroine. apparent.

M invention eompreheiuls an arrangement of parts for :'u'rom'plishing the. objects liereinat ttu set forth, oi". which the apparatus .desrrihed .is one embodiment, the. novel features oi the,iuvention heing more particularly pointed out in the appended claims.

in tl e dran ings: l igure. iis a perspec- .tive view of. an instrument emhodyiug my invention. The particular Instrument; shown in the drawings I have sometimes referred to, more or less arbitrarily asa horizmneter,

Fig. 2 is a perspt-rctivediagram on an en larger! scale of the optics oi the instrument shown in] Fig.1, together withcertain other coii vieratini elements. Figs.- 3, 4, 5, (5, 7, and 8 are diagramsillustratii'ig the use of the instrumentshown in Fig. 1. v

Like oharacters of reference throughout the several figures of the drawings indicate the same or similar elements.

. Referring now more particularly to the instrument which is shown in the drawings and which serves as an illustration of an embodiment of my invention: The numeral 1 denotes the body of the insti-iunent which is pivotall mounted in the standards 10 by means of the laterally extending trunnions 2 having reduced port-ions B which have hearings in the upper ends of the standards 10 in which hearings the said reduced portions of the trunnions are secured by the bearing caps 11. It, will be noted that but one'trnnnion and bearing is visible in thedrawings but it is evident that both may be and usually are identical.

'lhestundards 10 are mounted on a. base 12 which base may he integral with the plate 13 which plate is rotatable abouts verticalaxis due. to. the said plate being mounted on a suitable vertical hearing or pivot ..(not shown) such e. g. as provided for a surve vors transit. The pivot bearing for the. plate 13 may be mounted in the stand for the instrument of which the pedestal 14: and the tahlela, integral with the said pedestal, form a part. i

The base 12 is provided with an extension 16. which after heingoliset. in order to bring tivel v delicate means for turning; the instru ment about. its vertical axis is incorporated in the instrument aml -o1nprises a compare-- t-ively large gear 18 which is disposed hotween the plate [3 and the table laifand 15- preferably '1l.2.l (ll 1' secured to said table. 15.

i\leshin;r' with :the, gear-1S is a pinion which.

is mounted on a suitable spindle .(pinion and spindle not shown) the said spindle being journaled in' the boss 1G which boss is "formed integrally with extension 16, and the end of the-said pinion spindle terminating in the knot) or pinion-head 19. Thus the rotation of thepinion-head'19fslow1y rotates the instrument about its axis, the relat-ive speed depending on the relativ size of thehgear 18 mass cooperating panes,

Th instrument is provided at its forward end with two objectives 20 and 30 respectively, which are spaced apart in a direction transverse to their axes. The objective 20 is mounted in a tubular mount '21 which may be integral with a base portion The two vertical sides of the base are preferably beveled and fit snugly but easily in a doretailed slide 23, one of the inclined walls of which is 'n'm'ided by an adjusting gib 25. Thus the objective I20 and its mounting may be bodily raised and lowered, for a purpose hereinafter ex-- plained, and this movement o adjustment is controlled by the adjusting screws 26 and 27 which are threaded into the metal of the bod} 1 and respectively bear against the upper and lower portions or top and bottom of the base The objective 30 is mounted in a tubular mount 31 which may be integral with a base portion 3" flhe upper'and lower portions. or the top and bottom of this base portion are preferably beveled and fit snugly but easilyin a dove-tailed slide 33, one of the inclined walls of which is provided by an adjusting gib Thus the objective 30 and its mounting may be bodily shifted laterally for a purpose hereinafter explained, and this movement or adjustment is controlled by a rack and pinion mechanism comprising an extension 34, which extension passes through recess-land which is provided with teeth 313 which are engaged by a small pinion 3'7, mounted on the end of a shaft 38 which in journaled in the hearings 5, 5 and provided at its rear end with a knob 39.

In the diagram, Fig. 2 of the drawings, the objective :20 is indicated as vertically adjustable by the arrows adjacent thereto, the said arrows representing the slide-way and indicating the possible direction of adjustment. The horizontal arrows adjacent t e objective 30 in the same figure similarly indicate the horizontal adjust ment o'l objective 30.

Within the body of the instrmncnl'. and. adjacent its rear end is mounted a prism 40, which I will call an ocular prism. A desirable positioning of this prism may be. seen from Fig. 2 and will be hereinafter explained. 'lheprism 40 is j'n-et'crably adjustably mouutial. in any suitable well known manner all'ording'r universal adjust meat for initially j uz-ililulllllt2 the prisun in a sortol rcrtan ruhubox ll forming an ex tension of thc rnuJ' cud of the body 1 of the} instrument the member ll being rigidly \and wedge 80 with its base 81 up.

Hccurcd to the said rcar cm] of the instrulncnl; body. 'lbo ununbcr -l-l also carries the tclmcojrint ocular tubcs 51 and The tubc 51. which is a simple tube particularly designed to guide and carry the tube 52, is sccurcd to the rear face of the member 4'].

' 'lrinn which it projects in the direction of the longitudhial axis of the instrument. Within the tube are mounted an erecting system 50 and preferably a Ramsden ocu la r comprising the collective lens (30 and the eye. lens (51. A rack and pinion adjustment is provided to Facilitate the adjusting of the tubes 51 and a2 relatively to each other, the rack (not shown) bring preferably out in or mounted on the tube 52 and the pinion being rigidly mounted on the tube 51, as shown. Thus the erecting system and the eyepiece system which form an integral unit are bodily movable to and from the ocular prism l0 tor the purpose, a y. of adapting the instrument to eyes of different refractive IH'OIHltlCS. This condition is indicated in Fig. 2 by the bracket connectinp the elements ol the erecting sys tem and the eye-piece system. the adjacent arrow indicating that the unit is movable and also indicating the direction ol such movement.

The numeral 3+ indicates a 'l'orm ofthe usual eye shield provided for the comfort and bcnclit of the person using the instrument.

Referring now only to the instrlnncnt as thus far descrihevh presuming that its objectives fill and ll). its ocular prism ll), its erecting .systcm 50 and its ocular (ilk-bl, are all arranged substantially as indicated in Fig. 2 and presuming that it has been duly adjusted: This much of the instrument comprises what may be termed a simple azimuth telescope instru nn'ut and its field of view when trained on an object appears as represented in Fig. l, for example. the rectangle l l'1 representing the object sighted and the line I 'rc|u'cscntin;! a line which divides the field into two equal halves as shown. lhe line llis shown in Fig. 4 as hisectinl, the object llli which would indicate that the instrument is directly trained on the said object. This much of the. instrument alone howevcr, is incomplete and its functions adaptable to pra tical use are limited chiclly to the measuring: of angles in azimuth and in this respect the instrument forming-the subject of my present invention is adapted to use c. as a polio-us" instrument when suit-ably mounted on board ship. However in the complctc instrunuent shown 1 preferably intcrpose between the objectives 20 and 30 and the ocular prism -'-l() a pair of wedges and SH rns mctively. 'lhcse wedges are arranged as shown in Fig. the wedge 70 with its base Tl down 'lhcsn wedges are mounted togcthor in a carriage Ell) which carriage is suitably mounted on guide-ways so as to ho movable alone llllv axes of the objectives 20 and PM in the intervening! space between the said objectives and the ocular prism l The carriage calrics a suitable pointer 100 which eoiiperates with a suitable scale 110 in a manner and for purposes hereinafter explained. The long arrow in Fig. 2-shown adjacent the pointer lot) and the scale suggests the length of travel oi the wedges and indicates the. direction of their motion iorad'justment. Thedescription relating to the intmdi'letion of the wedges into the structure of the instrument has thus tar been rather general and has been confined somewhat for illustration to the Fig. 2 wherein the elements for simplicity and elearness sakehave been indicated in their-simplest or even in a conventional form. In this conneetion it will be noted that where the form or construction of certain elements shown in .Fig. 1 apparently diller i'rom those shown in Fig. 2 these shown in Fig. l are usually preferable.

In usual practice I may prefer to employ achronfiatic wedges oi circular eonstrut-tioin such as shown in Fig. 1 in dotted lines and indicated by the numerals and These wedges 1 preferably mount in a earriage l-"(J also shown in Fig 1, partly in dotted: lines. The.- upper portion of the (Jar.- ria e is provided with shoulders 14L whit-.11- extend laterally from a head portion 142. Qn'top of this head is secured the base plate 150. of the. bracket- ]51 that is designed to carry the variable length. pointer mornber 160. The under sid'e'ot' the base plate the-sides of the head portion 1'42 audit-he shoulders 1.41. form a. pair of" oppositely dis? posed rectangul arguide-ways; the uppersurface of the raised projection (tolthe body 1-; the'sides of ihe slot? throught-he said ])ro jeet-ion- (i and a finished surfaee withinthe. body (whieh surface. cooperates with: the shoulders 1.41) forming the guides alongw hich the above described guideavay'or': the carriage 140 slides, after the. manner of the cross head and. guides of a steam engine;

1-1;1ei 1m m: i Nil-denotes an inelined-jseale plate-which is mounted so asto. be longitudinally alinstable. To this end a sort of subtablel 1 having aninelined top which. nunsthe'lengthoi" the instrument and is provided eaelr. end with the stands 11-72 whereby the. said sub-table is secured totlie one :SidBfO'fithe top o i=the body 1 of= theinstnuni ent is'prov-ided'. 'Along'theupper sue faee -the,-.sub-t'able 1-71- runs ad'ove-tail groove in w-hielrfits the. dmesta'iled slide 173 which is secured to the under side of die. scale platelr'fla About midway along the loweredge off-the sub-tableliTl is formed, prefefablyintegral therewith, an extend- .-'1ng=-ea|' 174 which is fprovidial to support .tl1e Clamp plate 17.5.. This elamp plate atiits;

end-176 bears on the ear 174- and atits opposite-end bearson the. bevellTT'ol the srale plate 170. Bymeans oi the thumb srrew .178 which passes through the. clamp plate.

and'is threadecl-into tlieweariH. the-clamp plate. securely holds the scale plate 170 in any adjusted position to the top surface of the sub-table 171. In its normal position the srale plate and the. sub-table may he flush, thusiall'm'dint: a means for determinatiugthe normal position of the stale plate.

The hard 152 of the brarhet 1-31 is provided with a dove-tailed groove in 'whi'rh slides a dove-tail slide portion llil formed on the under side oi the pointer member Hill. The brarket head H2 is soiiu-lined aml disposed that the under side of the pointer memher 1H0 earried thereby lies in a plane that is parallel to the plane. oi the upper surl'are oi' the srale plate lit) and adjareut thereto and thus the iudieatiu point H33 will be unii ormly elose to the seale no-matter what relative position the seal" and pointer may oeeupy.

One side oi" the pointer uu-mber lot! is rovidtfd \'ith a rarlt llii-i' with \Vllltll meshes a pii'itoiilfll mounted on a spindle Hi5 whieh is journaled in the brarltet head 15:2 and which spindle is provided on its upper end with a h *ail..,l'(' (i whereby the indirating point 1-62 of member Hit) may readily be moved-transrersel-v Press thesrale-l'T-l). The. pointer member isluv then provided witlra srale 107 with. which eoiiywralfes an index l-51-l on the bracket headlFr-Ji For movingt-lierarriage Hi) and the ele ments carriedfihereliy along thegaxis of. the objeotives-JO and 3t) and for rigidly hold ingsame-in any adjustedposition I" prefer to provide the wormlo \vhi el r is threaded througlrthe-head l liol'; the carriage I-Hlas shown: 'Jhiswormis journuled in the. body of! the instrument at h at eaeh end'oi' the slot T. wherein the said wi-n'nr'sets ()n therear end ol'Yt'he. wornr \\.lli(ll is preferably provided with a= rediuwd end': portion (not shown is-mounted a bevel. gearli h, the hub. offthe said bevel gear andt'he shoulder at the. end of t'llfl' w=orm- (aa'i'perating: with the rear beu-ringf portion H tol'i-ntm. a thrust? bearing. for the worm 1'80; Mrs-hing. with-:hevel gear tH-l. isabevel-geaulrli w-hiehis mounted on aspindle (notshown) whieh spindle is j o'urnaledin. the boss [Hi3 oi the bearing bnaelu-t {H4 which lirarliet is seeured to andextends-rearwardly from a rear eorner oi the body. 1 as shown. )11. the opposite end ol' the spindle upon \v-hirli the gear- [82 is mounted'is serm'edthe.' hubof the erankhandle lHti whieh rranlt'is obviously torthe purposeoi rotating the. worm- ISO in a mannor that is-elearlyapparent.

'lhe'prinmry' filllt'tioll of the o .t-ieal systern of: t'l ii"-instrument,.best shown in Fig. 2 oift'he drawings, is toiorn'i an image of' an object, the two halves of which image may be relatively-displaced.

l'n-the present emhod-in'ient of my invem tionl p'reier to divii'le'tlie im a go'vertiCa-lly into the. two halves Rand L which halvestil 1 air Cit til

'lhe instrumenthaving been trained on an object, each of the objectives and re ccives a cone of image formingrays which cone of rays each objective transmits and retracts in passage. -The axial rays X and Y represent cones each of which cone will form a complete or whole image. In the further discussion of the light paths the path of the axial rays X and Y alone will be described. Having passed through the objectives the rays X and Y impinge on the perpendicular surfaces Tet and 84 of the respective wedges at 72 and 82 respectively. The rays X and Y pass on to the surfaces 75 and B5 respectively where they emerge at '73 and 53 the ray X being refracted downwardly and the ray Y being retracted upwardly. The rays X and Y passing through the front surface of the ocular prism 40 impinge on the primary reflecting surfaces 42- a'nd 4% respec' tively from which the said rays are inwardly reflected, the ray X continuin n to fall and the ray Y continuing to rise, as is clearly shown in Fig. 2, until the rays X and Y impinge on the secondary reflecting surfaces 4-l and 45 the intersection 46 of which surfaces is in the common focal plane of the objectives 20 and 30. It will he-noted that .the axial rays X and Y impinge on the inplementary halves of the image, as R and L in the drawings, and thuswhen the said half images are brought together a complete and perfect image is formed.

Since from $6 on only a half image is rel'l'ectcd, the rays X and T from 46 on are I designated a: and 1 respectively. Erom the rcllcrting surfaces 1H: and 45 on throughthe erecting system 50 the eyepiece (i061, the

path and action of the rays a: and 1 is deemed to be clearly apparent without further description. The field of view resulting from the course of the light rays just described in connection with Fig is shown in Fig; 5 it being presumed that the scale 100 is made for an object of 100 feet in height, that the object is 112,000 yards distant and that the object R-L in this case is 100 feet high.

Knowing the focal length of the objectives 2U aml 30 am] knowing one dimension of an object in a plane parallel to the focal plane of the objectives, 0. g. the height of an object. it we measure the height of the image we have'according to the law of magnification:

Focal lgn gth of objective (timesmght of object for all distances that are great as compared with the focal length of the objective. This formula ahtnallygives the distance of the object from the anterior focal point of the objective andthus if absolute accuracy is required, it is simply necessary to add the focal length of the objective. But since the focal length ol the objective is so extremely small as compared with the distance measured, it is a negligible increment and thus has been omitted as a term in the above equation.

Between the objectives :30 and 30 and thcinl'ocal plane wherein appears the two partjl'nage it-J1, I interpose the wedges T0 and H0 for the purpose of vertically displacing the two halves; it beingobvious that knowing the 1'i.*l'raeting angle ol the wedges and ha ng retracted the right portion it of the image'lt--li hall its height downwardly and having retracted the left portion L of the image ll--li hall its height upwardly s: that the top of the image portion R and the bottom. of image portion L coincide, see Fig. 5: l ran', by nu-asuriug the distance of the \icil-ge from the focal plane, accurately measmm Height of image ure the height of image l L, found on the focal plane of objectives 20 and 30. However, instead of-t-lre scale 110. measuring merely the distance of the wedges from the focal plane, the scale may be graduated in' terms of the size of the image or what is most preferable, the said scale may be graduated to read in terms of the distance of the objectsighted from thepbjective, as shown in Fig. 2, the scale 110 being supposed to be designed to read in yards of distance of object, the object in this case always being supposed to be 100 feet in. height.

A; study of the Fig. 2 will, in consideration with what has, been said, show that the nearer the object is, the farther from the focal plane and thenearer to the objectives,- the wedges 70 and 80 must be moved to-eflect coincidence and vice versa. When the inst-rlunent described is trained on an object that is atany distance and adjusted so that the two images are complementary and form iii) a complete image, the image in the field of the instrument looks as shown at R-L in Fig. -l the halving line D passing through the image as shown, and the range scale range coincidence lot member 100. this 1': lal'kerl 4 that the vertical adjustment of objective 2O is provided. lVhen' adjusting the instrument for infinity it is desirable to see that the wedge carrier 140 is not too near the end of its stroke since it is sometimes desirable that the wedges be movable in both directions from this point.

In order that the instrument be not limited in its application to objects of a certain height I provide for the instrument asea-le'170 the lower edge adjacent the bevel 177 being graduated for example for a 50 foot height of object and the opposite edge of the scale for a 150 foot height of object and by connecting the two scales with suitable inclined lines or curves, any straight line drawn along the scale parallel to beveled edge 177 will constitute a scale for some height between 50 feet and 150 feet depending on its position relative to the two longitudinal sides of the scale.

Cooperating with scale 170 is an adjustable pointer member 100, which, when the point 102 oi. the said membe egist'ers with the lower or 50 foot portion of; the scale 170, readsfiO'feet on scale 167 and when the pointer I62 registers with the upper or 150 foot portion of the scale 170, the scale 167 of the pointer member reads lotl feet. Suit,- able intermediate graduations are provided for the scale 167 so that the-instrument may beset for any height of object for instance, between 50 and 150 feet in height.

' The instrument herein described is particularly adapted. to use for range finding, spotting and the measuring angles in azimuth and forms avery COI'lVBillBlil] and reliable means for accomplishing these ends.

Innsing this instrument for range finding, an object or portion of an object is selected, and if its height be known or may be estimated the scale 1.67 is set accordingly, the instrument is trained on the object and the crank 186 is turned until the-image appears as shown in Fig. 5 which is the and the distance ,or range is read as indicated by pointer 102. In Fig. 1 of the drawings, the first 'line on the scale 170 is parallel to the'line of travel isthe infinity" and is INF. The measuring lines shown from' IN if down. may be considered to represent rcspectirety ranges of 75,000; amen; aspen; 15,000; 12,500; 10,000 0,500; 0,000; 8,500; 37,500; 5,000 and 4,000yds. Thus the pointer 162 in the p osi "011 shown in. Fig. 1. indicates a range of about 7,000 yards, the intermediate ranges between lines being in the present case, estimated. However other more exact known means may be provided. it on the other hand, the height of an object is not known andit is not suitable to estimate the height thereof, the instantaneous range may be obtained by an independent means such as any well known .range finder, the range coincidence efi'ected in the present instru ment by turning crank186 and then pinion head 166 turned until pointer 162 indicates I the range known after which the height adjustment may be maintained for all ranges of the same object.

In using the present instrument for spotting referring now particularly to Figs. 6, 7 and 8: The distance of the target. T from the ship B being known and the height of the observer at 0 being known; the instrument (located at O) is traihed on the object '1 as indicated by the line 0 T Fig. (3, and infinity coincidence of 'thetarget T is made as shown at '1 Fig. 7. The scale 167 is then set to'the height 0 B and the clamp 176' being loosened, the scale is slii'lted'until the-pointer 162 intersects the distance represented by B T, when the scale is clamped in place and the instrument is in readiness for spotting. The shot fired, the projectile falls at S Fig. 6 making the usual splash which shows in the field-of the instrument and is indicated by the line S in Fig. 7. Immediatelythe crank 180 is turned until coincidence otthe water line of half the target image Fig. 8 and half the splasiS in the same figure'isinadeas indicated in Fig. 8. The raz'ige. or distance indi catedby pointer 102 is tl'iedistance B S. The direction in which the crank 180 is to be turned is governed by whether the iumge of the splash S appears above or below the image of the target '1). It" the splash appears to be above the target and consequently the point S Fig. 6 is beyond the target T the wedges should be :InOVUll closer to the focal plane so that the distance will read greater than the distance 13 'l is known to be, and if the splash appears to be below the target the converse is true.

The manner in 'which the spotting is cliccted by this histrument is iml-icated clearly in Fig. (5 in which theline H is a horiZontal line parallel to the water line 15 T; 3? indicates the projection of; the point S on the plane of the target H P and. ll' S indicates the height of object on base line II T moved from T to S: The instrument described is placed at O. The figure 0 is considered to be a graphic solution of the problem met in spotting.

'The lateral adjustment of the objective 30 is provided to cure a condition of the image shown in Fig. '3 and may aptly be called the image separation" mljustment, the bringing of the objectives 20 and 30 closer together bringing the image halves to.- gether as is required in liig43, and the separation of the objectives JO-and 30 tending to separate the halves R and L.

For the purpose .of insuring a very fine and sharp dividing line D in the field 0f the instrument the ocular prism 4:0, in practiee, is made in two parts and cemented together. This is accomplished by making one of these parts a perfect rlnnnhoidof the same height and of the same thickness from front to back, t s the-prism all). and ha ving its ends inclined at an angle of lo degrees to its longitudinal axis. The eon'iplennmtary portion of the prism is made by cutting oil one of the acute extremities of a similar l'honr hoid from the center of the end surlaee at right angles theretinthe resulting prism thus. having one acutesingle beveled end and one blunt double beveled end. ()ne of the inelined end surfaces of the rhomhoid prism portion is silvered for'half the length from its blunt edge toward its acute edge. and to the remaining clear glass hall of this sur face. is eemented that surface of the double beveled end of the complementary portion of the prism that extends at right angles to the surface of its single beveled end. The Completed ovular prism. see l ig. 2. is in ell'eot one integral. pieee of glass since the cemented surfaees ol' the two parts of the prism are so cemented together that they have no optical ell'eet but transmit the light rays in the same manner as the glass of the. prism itself. Oneol theinelined end surfaces of therhomboidprismportion will thusprobably form the surface 43 of the finished oeu- Iar prism while hall of the vol'responding parallel nd surface of this rhomboid will form the surface 45. The surface. of the single beveled end of the. complementar v portion of this prism will form the. surface. El-2 and that surface of the double beveled end \\l)l('ll is parallel to the surface of the single beveled end and which preferably has been silver-ed. will form the rellertiug surface 44. Each of the leflert'iug surlaves ol the prism 40 may he silvered ii desired.

The usiug oi the herein described instrument as a pelorus" is believed to need no further description.

While the'prosent embodiment or my invention herein desvribed employs two optitnl wedge elements'oue on the axis of each objortive, it. will be. o served that one wedge 'element only might be used. it being feasible to dispose said wedge element on the axis of either objertive. in this case the brilliant-y of that portion oi the image \vhivh has to pass through the wedge would be somewhat sulalued as compared with the remaining portion of the image: only one half of the image would move on the "focal plane. so that greater travel of the wedges would lieneeesr sary for the. range adjustment: and the field oi view of the iustriuuent would not be utilized to as great advantage as in the present embmliun-nt. shown, because when range coincidence had been elleetod, the image would occupy an eccentric position in the field of View, especially in the ease of short ranges.

Having thus described a single embodiment of my invention what I claim and desire to secure by Letters Patent of the United States is:

1. In an optical instrument for measuring distances, the combination of a transversely adjustable objective, a second objective spaced from the first named objective in a direction substantially normal to the direc tion of the. adjustment thereof and adjustable toward and from said objective. of an oc-ular and an image uniting prism cooperating with the objeetive to form in the field of the instrument a single divided image of an objeel. comprising a pair of complementary half images received one. hal from each of the ohjeetives and arranged one on either sideol a dividing line. means operating be.-

tweeu the image uniting prism and the objectives and acting on the light transmitted by the latter to adjust the image halves one with relation, to the other to a greater or lesser extent. and means for translating the 99 displai-ement of the image halves into terms of range ol the object. I

*2. In an optiral instrluueutfor measuring distances. the combination of a transversely :uljustable objeetive. a second objective spaced from the first named objective in=a direetion substantially normal to the direction of the adjustment thereof and adjust able toward and from said objective. of an ocular and an image uniting prism cooperat- 100 ing with the objective to form in'the field of the instrument a single divided image. of an object. comprising a pair of complementary half images received one hall from each of the objertives and arranged one. on either' side of a dividing line. a pair of retracting wedges arranged one in the axis of earhobjeelive and mounted to he movable simultaneously along said axes. a rarriage for the wedges. an index earried therebyuud a seale cooperating with the index.

I In an optical instrument for measuring distant-es. the eomhination with an ocular and an image uniting prism having a pair of primary refleeting surfaces arranged at either end tliereol'.a1ula pair of interseeting seeoudarv relleetiug surl'ares arranged iutermediate the primary relleeting surfaeo with their iuterseetion in the axis of the ocular. of an ohjeetive lens arranged in line with each oil the primary rellerting surfaces of said prism said objeetives each being individually adjustable in a dirertion disposed at right angles to thedirertion of adjustment of the other and transversely to their axes, means operating between the image. uniting prism and the objectives, and acting on thelight transmitted thereby to shift the imafe -formed by one objective. with relation to the image. formed by the. other,

, prism and an ocular system cooperating with said ob ectives to form a slngle image,

4;. In an'optical instrument for measuring distances, the combination with a pair of transversely spaced obj ectives'each adapted to forman image of an object, an ocular and an image uniting prism adapted to lect complementary halves of each of said images and unite them inthe, field, of the ocular as a single dividedimage, of optical means for relatively adjusting the image halves in the field of the ocular said means including a refracting wedge arranged in the axis of one of the objectives and adapted to move along said'axis between the objective and the image uniting prisnr, a car'- rier for said refra-cting wedge, an index.

traveling with the carrier, a scale codperating with the index, said scale and index be ing relatively adjustable in the direction of travel of the latter to-se'tthe instrument for the measurement of the range 'of the second object in the field by alining the half image onh one' object with the half image of the ot cix- 5. An instrument of the class described embodying a pair of objectives, an ocular a pair of optical Wedges arranged one along the axis of each objective and adapted to retract the images formed by the respectiveobjectives in 'opposite'directions, a carriage foi the said vedges mounted to be movable along the axes of the objectives, guiding means for the carriage, a pointer mounted on said carriage, said pointer being ad ustable in a direction transverse to the direction of movement 'ofthe wedge carriage and a scale cooperating with said pointer said. scale comprising a plate provided with divergent lines extending in a direction transverse tothe direction ofmovement of the "the images of the respective objectives in opposite directions, a carriage for'the said wedges mounted to be movable along the axes of the objectives, guiding means for the carriage,- a pointer mounted on said ourriage said pointer being adjustable in a div rection transverse to the direction of movement of the wedge carriage, a scale cooperating with said pointer said scale-comprising a plate provided with divergent-lines ex tending in a direction transverse-to the direction of movement of the said wedge carriage, and means whereby the scale may be. adjusted in the direction of movementof the said wedge carriage, substantially asand for thepurposes herein set forth.

.7. In an optical instrument for measuring distances, the combination with a pair of objective lenses having a "common focal plane and each adapted to form one of a pair ct images. of a. common object, means acting on thelight transmitted by the objecs ti'ves'to shift-the images formed thereby in the focal -plane,,fone with relation to the other and an ocular, of an image'uniting prism provided at. each of itsends with a rimary reflecting. surfaceadapted torevceive light from one of the objectives, and to refiectit inwardly, and having a pair of intersecting secondary reflecting surfaces arranged intermediate the rimary refieeting surface in the path of light reflected thereby with their intersecting edge disposed in the axis of the ocular and extendmg in the direction of movement of the images, said secondary surfacesbeing adapted to receive coniplen'ientary portions of the images formed by the objectives and to unite them as a single divided whole image.

8. In an optical instrument for measuring distances-, the combination with a pair of ob-' ectlve lenses arranged along transversely spaced axes and an ocular, of an image uniting ocula'r prism having a pair of inwardly facing converging reflecting surfaces arranged one in the axis of each of the objectives-anda pair of intersecting outwardly facing reflectlng surfaces arranged intermediate the first named reflecting surface and in theaxis of the ocular whereby complementary halves of the image of a common object formed by the objective are presented to the ocular one onxeach' side of a straight central dividing line extending across the field of the instrument, adjustable refracb ing means operating in the path of light be tween the ocular prism and the objective to move the image halves relatively in the direction of the dividing line until opposite extremities of the image are brought into alinement and means for determiningthe extent of the image displacement by the re- -fracting means in terms of the distance of the object from. the instrument.- Y

BRADLE Y.A. FISKE.

Witnesses B. F. McCA-r, Cnas. BAn'rz. 

